The present invention relates to seismic retrofitting of soft story buildings. Soft story buildings are multi-story, wooden framed structures, typically having two to four floors, and wide doors or other large openings. These structures were built in the 1950s, '60s and '70s and typically used for apartments and condominiums and with large openings on the ground floor providing the entrance to a parking garage. This configuration also is referred to as “tuck-under” parking. To maximize the number of parking spaces, such buildings typically have little or no walls on the exterior line of the first story. Soft story buildings are very vulnerable to collapse in moderate to severe earthquakes and were responsible for a substantial number of the homes that became uninhabitable in California's Loma Prieta earthquake of 1989 and the Northridge earthquake of 1994, among others. As a result, San Francisco, and more recently Los Angeles, have adopted ordinances targeting soft story apartment buildings and requiring retrofitting by reinforcing the “soft-story” condition. Several other cities and municipalities in California are following suit. Current California building codes now require that the exterior line of columns in tuck-under parking areas be designed with sufficient strength and stiffness to prevent their collapse. In some cases, the wooden beams in soft story buildings are supported by columns formed of steel tubing typically four inches or less in diameter. Such structures also are referred to as soft story buildings and also are very vulnerable in earthquakes. Newer buildings having tuck-under parking typically use conventional steel moment frames instead of wood columns and beams in the tuck-under portion of the structure.
To comply with the ordinances requiring seismic retrofitting of soft story buildings, the conventional solution has been to construct a new steel frame under the existing building adjacent to the existing wooden frame. The new steel frame is independent and separate from the original building's wood frame. The additional columns of conventional steel framing while providing the required seismic support, occupy additional space and thus reduce clearance for parking. Their installation frequently requires construction of a new foundation below the supporting columns as well as the connection of the new frame to the existing structure to adequately transfer seismic loads from the building to the new frame. The construction and installation of these added steel structures is time consuming and thus very disruptive, is difficult to install and thus expensive and the result, while workable, is somewhat inefficient.
The frame assembly of the present invention provides the support necessary to comply with the new retrofit ordinances in California while obviating the shortcomings in the current retrofitting practices.